This present invention relates to bearings in general, and in particular to a bearing assembly including rolling elements.
A bearing is generally a device used to reduce friction between moving surfaces and to support moving loads. One common type of bearing is a rolling element bearing that typically includes an outer ring, inner ring, and rolling elements. The outer ring is larger in diameter than the inner ring such that a number of rolling elements, in the form of solid balls or rollers, are placed at equal intervals in the open space between the two rings. The rolling elements often rotate between an inner and outer race that include a ball or roller path positioned within the inner and outer ring, respectively. More specifically, the inner race includes the ball or roller path positioned within the inner ring at the outside diameter. The outer race includes the ball or roller path positioned within the outer ring at the inner diameter. The rolling elements may include small steel balls, cylindrical, or conical rollers, depending on the particular application. The rolling elements assist in distributing and reducing friction through the movement of the bearing.
A rolling element bearing that utilizes rolling elements in the form of balls is often referred to as a ball bearing. In the ball bearing, a number of balls rotate freely around the inner ring positioned between the inner race and an outer race. The inner ring is often rigidly fixed to a rotating shaft, and the outer ring can be unsupported or conversely rigidly fixed to a support. The balls are generally held in position between the inner and outer races by a cage or separator that serves to keep them evenly spaced and to prevent them from contacting each other. A rolling element bearing that utilizes rolling elements in the form of rollers is similar to the ball bearing, except that in place of the balls are generally steel cylinders or rollers.
Typically, rolling element bearings attempt to transfer or balance a load between the inner and outer races. This transfer of load may occur utilizing only a portion of the rolling elements, especially those rolling elements in closest proximity to the radial location of the load, or the radial load zone. This uneven, or concentrated load distribution can cause the central rolling element, the element in the closest proximity to the radial location of the load, or rolling elements nearest the central rolling element, to carry most, if not all, of the load. This can undesirably limit the life of the bearing and the maximum load it can carry by centralizing the load on only a few of the rolling elements.
Although rolling element bearings undergo uneven and sometimes concentrated load distribution, certain types of bearings are more susceptible to a reduced life or reduced load capacity than other types of rolling element bearings. For example, a well known rolling element bearing referred to as a cam follower bearing, with an unsupported outer ring, tends to concentrate the load on the central rolling element more heavily than do other types of bearings. However, spreading the load, which is distributing a portion of the load through rolling elements adjacent to those moving through the radial load zone, can assist in reducing the maximum load received by each rolling element, in particular the central rolling element. Theoretically, an increased radial load zone might extend bearing life and consequently increase the maximum load support capability for a rolling element bearing including the cam follower type.
Some have attempted to implement this theoretical technique of increasing the radial load zone to extend bearing life or increase the maximum load support capability by forming an elliptical inner race. One arrangement for spreading the load in a bearing, in which the load is applied in an established direction defining a predetermined radial zone, is provided in U.S. Pat. No. 3,321,256 to Orain. Orain discloses a bearing with an inner race having a substantially elliptical cross section. The bearing attempts to attain a higher load capacity by more evenly distributing load over the rollers in the load zone. Orain mentions approximation of an elliptical profile by locally increasing the radius of curvature of the inner race by eccentric machining. However, Orain limits such approximate elliptical profiles to those which do not prejudice the continuity of the surface of the inner race, and sectors of differing curvature are made to smoothly merge. Machining smooth transitions between race sectors of differing curvature adds greatly to the manufacturing complexity and cost of the bearing.
Another arrangement for spreading the load in a bearing, in which the load is applied in an established direction defining a predetermined radial loading zone, is provided in U.S. Pat. No. 4,067,626 to McElwain. McElwain discloses a universal bearing joint that utilizes a bearing cup having an inner race formed in the shape of an ellipse. The lesser diameter of the elliptical surface is generally disposed 90xc2x0 from the maximum loading point to attempt to distribute the load over many needle bearing elements. Although the elliptical surface assists in increasing the life of the bearing, the elliptical surface requires extensive and elaborate manufacturing processes, and does not provide a sufficient distribution of the load.
In yet another arrangement, U.S. Pat. No. 4,909,641 to McKenzie discloses a bearing with an expanded load zone by utilizing an inner race supported by an elastically deformable body. The bearing includes a non-rotating ring which has an elastomer of non-uniform thickness bonded to it. The non-uniform thickness of the elastomer causes the inner race to go out of round and deform when under load, attempting to reduce maximum rolling element stress. However, manufacturing this type of bearing also requires extensive and elaborate manufacturing processes, and the elastomer does not provide sufficient strength or durability to provide an ideal solution.
While the above non-circular inner races tend to more evenly share loads among the rollers in the radial load zone of the bearing, each requires elaborate manufacturing processes to produce an elliptical race, some even require introduction of an elastically deformable body and are otherwise deficient in providing an optimum load distribution. Often, these elaborate manufacturing processes and materials undesirably increase the cost of the bearing to a consumer. Using these less durable, and less than optimal load distribution techniques, a consumer may then undesirably choose larger bearings to handle the heavier loads, which may result in larger and more expensive than necessary bearings, and further result in failed bearings more often.
Thus, there is a need for a bearing that can more optimally and evenly share the load among a set of rolling elements in the bearing load zone to reduce maximum roller load on any one rolling element.
The present embodiments provide the ability to more optimally and evenly share a load among a set of rolling elements to reduce maximum roller load in a cost effective and efficient manner. The present embodiments are illustrated as exemplary embodiments that disclose a system and method for reducing the maximum load on the central rolling element in such bearings.
In an aspect of the present embodiment, a bearing generally includes an annular outer race and an inner race, where the inner race includes a constant first outer radius and a second outer radius in a given plane perpendicular to the axis of rotation of the bearing. In an exemplary embodiment, the second outer radius forms an eccentric section that is positioned under the bearing load. Also included in this exemplary embodiment, are rolling elements positioned between the inner and outer races, where the bearing load on the set of the rolling elements located at the eccentric section is distributed to adjacent rolling elements.
In another aspect of the present embodiment, an inner ring has an inner race generally including a first outer radius and an eccentric section having a second outer radius that is larger than the first outer radius wherein the second outer radius provides the eccentric section extending past the limits of the bearing load zone, and wherein the eccentric section has a center of curvature offset with respect to the center of curvature of the first outer radius.
The present embodiments provide the ability to more evenly and optimally share the load among a set of rolling elements to reduce maximum roller load in a bearing in a cost effective and efficient manner. The present embodiments utilize a circular inner race over much of the outer surface, but includes an eccentric section having a slightly greater radius of curvature, and having a center of curvature offset with respect to the center of curvature of the outer surface of the remainder of the inner race. Utilizing the present embodiments, the load is more evenly and optimally shared among the rolling elements in the bearing load zone which reduces the maximum roller load, and increases fatigue life of the bearing. Such a bearing or bearing assembly does not require the introduction of an elastically deformable body or an elliptical inner race, and does not require expensive machining of smooth transitions between race sections of differing curvature.
The foregoing and other objects, features and advantages of the bearing or bearing assembly will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings.